One half of the marbles are red a third are white the other 6 are blue

1/2 + 1/3 = 3/6 + 2/6 = 5/6so 5/6 of the total marbles are red and white.
That means 1/6 are blue. So if 6 are blue, then 1/6 of the total marbles = 6

1/6x = 6
x = 6 * 6/1
x = 36there are 36 total marbles

1/2 are redso 1/2(36) = 36/2 = 18 are red
1/3 are white1/3(36) = 36/3 = 12 are white
and 6 are blue.